Vehicles comprising an internal combustion engine are subjected to a plurality of different legislative requirements and regulations. Some of these requirements and regulations are directed to fuel consumption and exhaust emission. Different countries or markets may have different requirements. One measure that is used to reduce fuel consumption is to provide the vehicle with a start/stop function, which allows the combustion engine to be shut off when the vehicle is stopped, e.g. at a traffic light or in a queue.
Due to the start/stop function, a larger and more powerful battery is required in order to be able to run the starter motor more often. The start/stop function may also, especially in cold weather conditions, cause a voltage drop below e.g. 10.5 volts, which may be considered as the minimum allowable voltage for the electrical system of the vehicle. A voltage above 10.5 volts is required to ensure that all electronic control units function properly. Instead of using one larger and more powerful battery, this problem is often solved by using a second smaller auxiliary battery that will only power the electrical system of the vehicle during start of the engine, such that the voltage drop of the starter battery does not affect the electrical system.
In modern cars, the packing situation in the engine compartment is such that the battery does not fit in the engine compartment, which used to be the regular place for the battery. Normally, the main battery is placed at the rear of the vehicle, and the auxiliary support battery is placed at the front of the vehicle, e.g. in the engine compartment. This requires long and thick cables to transfer the needed current to and from the main battery.
In order to reduce the electrical losses, it is becoming more and more common to use an additional 48 volt system for the high current components of the vehicle, e.g. for the starter motor. The 48 volt battery is also placed at the rear of the vehicle, together with the main battery, while the high current loads are positioned mainly at the front of the vehicle. The high current loads include e.g. the starter motor, the servo motor for the power steering and the automatic brake system. These loads will require a high current and also a high peak current.
There is thus room for an improved voltage supply unit for a vehicle.